1. Field of the Invention
The invention relates to a method for a circular grinding of a workpiece and to an apparatus for carrying out the circular grinding method.
2. Background of the Invention
Many applications require workpieces which are at least partially of rotationally symmetrical design and have a workpiece axis defining the axis of symmetry and also two adjacent faces which are designed to be rotationally symmetrical with respect to the workpiece axis and between which is formed a circular transition edge. Such workpieces are used, for example, as valve needles or nozzle needles, typically one of the two faces forming a sealing seat and the other of the two faces forming a guide face on the valve needle or nozzle needle. So that such valve needles or nozzle needles can be used even for high-pressure applications, such as, for example, fuel injection systems for modern petrol or diesel engines, where sometimes pressures of well above 1000 bar have to be controlled, high requirements must be satisfied in terms of adherence to manufacturing tolerances. In particular, the transition edge between the seat face and the guide face must be formed so as to be as sharp-edged and as burr-free as possible.
Workpieces of the abovementioned type are machined using circular grinding by using circular grinding machines for carrying out the circular grinding methods.
The publication WO 01/60565 (Robert Bosch GmbH) disclosures a circular grinding method and a circular grinding machine which makes it possible to produce a valve needle for a fuel injection valve by means of circular grinding. The circular grinding machine is provided with a grinding wheel and with a deburring mandrel arranged opposite the grinding wheel with respect to the workpiece. When the grinding wheel grinds a grinding face of the workpiece, a burr occurs, which projects beyond the transition edge formed between this grinding face and an adjacent face into the region of the adjacent face. The deburring mandrel is arranged and designed in such a way that the burr is pressed back onto the grinding face by the deburring mandrel as a result of the rotation of the workpiece rotating about its axis and is ground down during the next contact with the grinding wheel.
It became apparent that the circular grinding method and the circular grinding machine according to the publication WO 01/60565 have disadvantages in terms of the mass production of large workpiece series. To be precise, it repeatedly happens that burr formation is not reliably prevented by the deburring mandrel. A complicated rechecking of the workpieces is therefore necessary so that the desired manufacturing quality can be ensured.